Tail gas of gas fermentation to dry gasification feedstock

Abstract

The disclosure provides for the integration of a gas fermentation process with a gasification process whereby tail gas from the gas fermentation process is recycled to a dryer of the gasification process. The tail gas from the gas fermentation process is utilized to generate heat which in turn is used to dry feedstock to the gasification process. The heat is typically used to heat a drying gas, such as air, which is then directly or indirectly contacted with the gasification feedstock to dry the gasification feedstock. Dried gasification feedstock provides improved yield and improved quality of syngas as compared to gasification feedstock that is not dried.

The invention claimed is: 
     
       1. A method comprising:
 a) heating a drying gas; 
 b) providing the heated drying gas to a dryer containing a gasification feedstock, and directly contacting the drying gas with the gasification feedstock to generate a dried gasification feedstock; 
 c) passing at least a portion of the dried gasification feedstock to a gasification process, and gasifying the dried gasification feedstock to generate syngas; 
 d) fermenting at least a portion of the syngas in a bioreactor using a microorganism to generate tail gas, and a fermentation broth comprising at least one product and microbial biomass comprising the microorganism; 
 e) passing the fermentation broth to a product recovery process to produce a microbial biomass depleted water stream, a crude ethanol stream, a fusel oil stream and a product stream, wherein microbial biomass comprising the microorganism is separated from the fermentation broth; 
 f) drying at least a portion of the microbial biomass comprising the microorganism; 
 g) passing at least a portion of the dried microbial biomass of step (f) to the gasification process gasifying the dried microbial biomass to generate syngas, and sending the syngas to the bioreactor of step (d), and further passing at least a portion of a stream selected from the microbial biomass depleted water stream, the crude ethanol stream, the fusel oil stream, and any mixture thereof to the gasification process; and 
 h) utilizing at least a portion of the tail gas to provide heat for heating the drying gas. 
 
     
     
       2. The method of  claim 1 , wherein the gasification feedstock is sorted municipal solid waste, unsorted municipal solid waste, industrial solid waste, agricultural waste, forest waste, lignocellulosic material, sewerage, sludge from wastewater treatment, or any combination thereof. 
     
     
       3. The method of  claim 1 , wherein the tail gas comprises carbon dioxide. 
     
     
       4. The method of  claim 3 , wherein the tail gas further comprises carbon monoxide, hydrogen, nitrogen, and methane. 
     
     
       5. The method of  claim 1 , wherein the microorganism is one or more C1-fixing microorganism. 
     
     
       6. The method of  claim 5 , wherein the C1-fixing microorganism is selected from  Moorella, Clostridium, Ruminococcus, Acetobacterium, Eubacterium, Butyribacterium, Oxobacter, Methanosarcina, Desuljotomaculum , and any combination thereof. 
     
     
       7. The method of  claim 1 , wherein the drying gas is air. 
     
     
       8. The method of  claim 1 , wherein the gasification process produces a greater yield of syngas as compared to gasification without drying the gasification feedstock. 
     
     
       9. The method of  claim 1 , wherein the gasification process produces a greater quality of syngas as compared to gasification without drying the gasification feedstock. 
     
     
       10. The method of  claim 1 , wherein the tail gas is burned to provide heat for heating the drying gas. 
     
     
       11. The method of  claim 1 , wherein the microbial biomass depleted water stream which is passed to the gasification process. 
     
     
       12. The method of  claim 11 , wherein the H 2 :CO ratio of the syngas from the gasification process is increased to at least 2:1. 
     
     
       13. The method of  claim 1 , wherein at least 92% of energy in the tail gas is recovered. 
     
     
       14. A method comprising:
 a) heating a drying gas; 
 b) providing the heated drying gas to dryer containing gasification feedstock, and directly contacting the drying gas with the gasification feedstock to generate a dried gasification feedstock; 
 c) passing at least a portion of the dried gasification feedstock to a gasification process, and gasifying the dried gasification feedstock to generate syngas; 
 d) fermenting at least a portion of the syngas in a bioreactor using a microorganism to generate tail gas, and a fermentation broth comprising at least one product and microbial biomass comprising the microorganism; 
 e) passing the fermentation broth to a product recovery process to produce a microbial biomass depleted water stream, a crude ethanol stream, a fusel oil stream and a product stream, wherein microbial biomass comprising the microorganism is separated from the fermentation broth; 
 f) drying at least a portion of the microbial biomass comprising the microorganism; 
 g) passing at least a portion of the dried microbial biomass of step (f) to the gasification process gasifying the dried microbial biomass to generate syngas, and sending the syngas to the bioreactor of step (d), and further passing at least a portion of a stream selected from the microbial biomass depleted water stream, the crude ethanol stream, the fusel oil stream, and any mixture thereof to the gasification process; and 
 h) utilizing at least a portion of the tail gas to provide heat for heating the drying gas; 
 i) generating a microbial biomass depleted water stream from the product recovery process and passing the microbial biomass depleted water stream to the gasification process thereby increasing the H2:CO ratio of the syngas from the gasification process to at least 2:1. 
 
     
     
       15. The method of  claim 14 , wherein at least 92% of energy in the tail gas is recovered. 
     
     
       16. A method comprising:
 a) heating a drying gas; 
 b) providing the heated drying gas to dryer containing gasification feedstock, and directly contacting the drying gas with the gasification feedstock to generate a dried gasification feedstock; 
 c) passing at least a portion of the dried gasification feedstock to a gasification process, and gasifying the dried gasification feedstock to generate syngas; 
 d) fermenting at least a portion of the syngas in a bioreactor using a microorganism to generate tail gas, and a fermentation broth comprising at least one product and microbial biomass comprising the microorganism; 
 e) passing the fermentation broth to a product recovery process to produce a microbial biomass depleted water stream, a crude ethanol stream, a fusel oil stream and a product stream, wherein microbial biomass comprising the microorganism is separated from the fermentation broth; 
 f) drying at least a portion of the microbial biomass comprising the microorganism; 
 g) passing at least a portion of the dried microbial biomass of step (f) to the gasification process gasifying the dried microbial biomass to generate syngas, and sending the syngas to the bioreactor of step (d), and further passing at least a portion of a stream selected from the microbial biomass depleted water stream, the crude ethanol stream, the fusel oil stream, and any mixture thereof to the gasification process; and 
 h) utilizing at least a portion of the tail gas to provide heat for heating the drying gas wherein at least 92% of energy in the tail gas energy is recovered. 
 
     
     
       17. The method of  claim 16 , wherein the microbial biomass depleted water stream is passed to the gasification process. 
     
     
       18. The method of  claim 17 , wherein the H 2 :CO ratio of the syngas from the gasification process is increased to at least 2:1.